The present invention relates generally to devices and methods used in conjunction with cardiopulmonary resuscitation procedures. In particular, the present invention relates to devices and methods for increasing cardiopulmonary circulation in patients with severe low blood pressure or cardiac arrest.
Worldwide, sudden cardiac arrest is a major cause of death and is the result of a variety of circumstances, including heart disease and significant trauma. In the event of a cardiac arrest, several measures have been deemed to be essential in order to improve a patient""s chance of survival. These measures must be taken as soon as possible to at least partially restore the patient""s respiration and blood circulation. One common technique, developed approximately 40 years ago, is an external chest compression technique generally referred to as cardiopulmonary resuscitation (CPR). CPR techniques have remained largely unchanged over the past three decades.
With traditional CPR, pressure is applied to a patient""s chest in order to increase intrathoracic pressure. An increase in intrathoracic pressure induces blood movement from the region of the heart and lungs towards the peripheral arteries. Such pressure partially restores the patient""s circulation. Traditional CPR is performed by actively compressing the chest by direct application of an external pressure to the chest. After active compression, the chest is allowed to expand by its natural elasticity which causes expansion of the patient""s chest wall. This expansion allows some blood to enter the cardiac chambers of the heart. The procedure as described, however, is insufficient to ventilate the patient. Consequently, conventional CPR also requires periodic ventilation of the patient. This is commonly accomplished by mouth-to-mouth technique or by using positive-pressure devices, such as a self-inflating bag which relies on squeezing an elastic bag to deliver air via a mask, endotracheal tube or other artificial airway.
In order to increase cardiopulmonary circulation induced by chest compression, a technique referred to as active compression-decompression (ACD) has been developed. According to ACD techniques, the active compression phase of traditional CPR is enhanced by pressing an applicator body against the patient""s chest to compress the chest. Such an applicator body is able to distribute and apply force substantially evenly over a portion of the patient""s chest. More importantly, however, the applicator body is sealed against the patient""s chest so that it may be lifted to actively expand the patient""s chest during the decompression step. The resultant negative intrathoracic pressure induces venous blood to flow into the heart and lungs from the peripheral venous vasculature of the patient.
Also of importance to the invention are ventilation sources that are used in connection with CPR techniques to properly ventilate the patient. One type of ventilation source is the AMBU bag available from AMBU International, Copenhagen, Denmark. The AMBU bag can also be used in connection with a positive end-expiratory pressure (PEEP) valve, available from AMBU International, to treat some patients with pulmonary and cardiac diseases. However, until the present invention, a positive end-expiratory pressure valve in connection with a ventilation source has not been used with any CPR techniques.
With both traditional CPR and ACD-CPR techniques, an increase in the amount of venous blood flowing into the heart and lungs from the peripheral venous vasculature would be desirable to increase the volume of oxygenated blood leaving the thorax during the subsequent compression phase. It would therefore be desirable to provide improved methods and apparatus for enhancing venous blood flow into the heart and lungs of a patient from the peripheral venous vasculature during both conventional CPR and ACD-CPR techniques. It would be particularly desirable to provide techniques which would enhance oxygenation and increase the total blood return to the chest during the decompression step of CPR and ACD-CPR, more particularly of ACD-CPR. This can be accomplished according to the present invention by augmentation of both negative and positive intrathoracic pressure, thereby amplifying the total intrathoracic pressure swing. An invention for providing this crucial improvement is described.
Severe hypotension or very low blood pressure can lead to passing out and in some circumstances cardiac arrest. Like cardiac arrest, patients with low blood pressure often suffer from insufficient blood returning to the heart after each beat. This results in a decrease in forward blood flow out of the heart and eventually to low blood pressure. It would therefore be desirable to provide techniques or devices that would increase venous blood flow to the heart when a person suffers from low blood pressure. According to the invention, such an approach could help return blood flow to the heart and result in an increase in blood flow to the vital organs.
ACD-CPR techniques are described in detail in Todd J. Cohen et al., Active Compression-Decompression Resuscitation: A Novel Method of Cardiopulmonary Resuscitation, American Heart Journal, Vol. 124, No. 5, pp. 1145-1150, November 1992; and Todd J. Cohen et al., Active Compression-Decompression: A New Method of Cardiopulmonary Resuscitation, The Journal of the American Medical Association, Vol. 267, No. 21, Jun. 3, 1992. These references are hereby incorporated by reference.
The use of a vacuum-type cup for actively compressing and decompressing a patient""s chest during ACD-CPR is described in a brochure of AMBU International A/S, Copenhagen, Denmark, entitled Directions for Use of AMBU(copyright) Cardiopump(trademark), published in September 1992. The AMBU(copyright) Cardiopump(trademark) is also disclosed in European Patent Application No. 0 509 773 A1. These references are hereby incorporated by reference.
According to the invention, methods and devices for increasing cardiopulmonary circulation are provided. The methods and devices may be used in connection with any generally accepted CPR methods or with active compression decompression (ACD) CPR techniques. Preferably, the methods and devices will be used in connection with ACD-CPR. In one aspect, they may be used in patients with severe low blood pressure and who are not in cardiac arrest and breathe spontaneously.
Cardiopulmonary circulation is increased according to the invention by impeding airflow into a patient""s lungs during the CPR decompression phase or during a spontaneous inhalation. This increases the magnitude and prolongs the duration of negative intrathoracic pressure during in the patient""s chest, i.e., increases the duration and degree that the intrathoracic pressure is below or negative with respect to the pressure in the peripheral venous vasculature. By enhancing the amount of venous blood flow into the heart and lungs, since equilibration of intrathoracic pressure during decompression occurs to a greater extent from enhanced venous return rather than rapid inflow of gases into the chest via the patient""s airway, cardiopulmonary circulation is increased.
In a specific embodiment, impeding the airflow into the patient""s lungs is accomplished by decreasing or preventing ventilation during the decompression phase of CPR. The method employs the use of a flow restrictive or limiting member, such as a flow restrictive orifice disposed within or connected in series with a lumen of a ventilation tube, or a pressure-responsive valve within a lumen of the tube to impede the inflow of air. The pressure-responsive valve is biased to open to permit the inflow of air when the intrathoracic pressure falls below a threshold level. In order to properly ventilate the patient, the method preferably provides for periodically ventilating the patient through the ventilation tube after compression of the patient""s chest. When periodic ventilation is performed, gases can be delivered either through the impeding step or in another embodiment they can bypass the impeding step. In some cases, an oxygen enriched gas may be supplied to the patient through the pressure-responsive valve once this valve opens.
An exemplary embodiment provides for covering the patient""s mouth and nose with a facial mask. This mask contains means for impeding airflow into the patient""s airway during decompression of the patient""s chest, e.g. either an orifice or valve as just discussed.
A specific embodiment further provides means for impeding air from leaving the lungs during compression of the patient""s chest to further enhance cardiopulmonary circulation by enhancing positive intrathoracic pressure during the compression phase.
When performing cardiopulmonary resuscitation to enhance circulation according to the invention, an operator compresses a patient""s chest to force blood out of the patient""s thorax. The patient""s chest is then decompressed to induce venous blood to flow into the heart and lungs from the peripheral venous vasculature either by actively lifting the chest (via ACD-CPR) or by permitting the chest to expand due to its own elasticity (via conventional CPR). During the decompression step, airflow is impeded from entering into the patient""s lungs which enhances negative intrathoracic pressure and increases the time during which the thorax is at a lower pressure than the peripheral venous vasculature. Thus, venous blood flow into the heart and lungs from the peripheral venous vasculature is enhanced. This is because the intrathoracic pressure equilibrium during decompression occurs as a result of enhanced venous return rather than from inflow of air via the trachea. In a particular embodiment, compression and decompression of the patient""s chest may be accomplished by pressing an applicator body against the patient""s chest to compress the chest, and lifting the applicator to actively expand the patient""s chest.
An apparatus for enhancing cardiopulmonary circulation according to the method comprises an improved endotracheal tube having a flow restrictive element for impeding airflow from the patient""s lungs during chest decompression. A second apparatus according to the invention provides for an improved air-delivery system comprising a compressible structure having a flow restrictive element included in or attached to an opening of the compressible structure to impede the flow of gases to the patient""s lungs. Also, a connector is provided for interfacing the compressible structure to the patient, preferably by attaching a facial mask or endotracheal tube to the structure.
In another aspect of the invention, a valving system is provided for regulating airflow into a patient""s lungs when performing cardiopulmonary resuscitation. The system includes a housing having an upstream region and a downstream region. A means is provided between the upstream region and the downstream region for inhibiting air from flowing from the upstream region to the downstream region when the pressure in the downstream region is less than the pressure in the upstream region. In this manner, air is inhibited from flowing into the patient""s lungs during decompression of the patient""s chest thereby forcing more venous blood into the chest and enhancing vital organ perfusion. A means is further provided for allowing air to flow into the downstream region when ventilating the patient. In this way, adequate ventilation can be provided to the patient during the procedure.
In one particular aspect, the inhibiting means comprises a valve which inhibits airflow from the upstream region to the downstream region when the pressure in the downstream region is less than the pressure in the upstream region. The valve preferably includes a diaphragm which is closed when the pressure in the downstream region is less than or equal to the pressure in the upstream region. Such a configuration prevents air from flowing into the patient""s lungs during decompression of the patient""s chest while allowing air to be exhausted from the patient""s lungs during compression. Preferably, the diaphragm is constructed of a flexible membrane. Alternatively, the diaphragm can be constructed using a ball.
In another particular aspect, the diaphragm is biased to open when the pressure in the downstream region is about 2 cm H2O or greater, and more preferably at about 2 cm H2O to 10 cm H2O. Biasing of the diaphragm in this manner increases intrathoracic pressure during compression of the patient""s chest to further enhance vital organ perfusion.
In still a further aspect, the means for allowing air into the downstream region includes a means for opening the diaphragm when air is injected into the upstream region to ventilate the patient. The means for opening the diaphragm preferably includes an ambient pressure region that is adjacent the diaphragm. When air is injected into the upstream region, the pressure within the upstream region increases thereby drawing the diaphragm into the ambient pressure region and allowing the air to flow to the patient""s lungs.
In yet another aspect, the means for allowing air into the downstream region includes a manually operable valve at the downstream region which is manually opened to allow air to flow into the downstream region upon return of spontaneous circulation. In this manner, a rescuer can manually open the valve when the patient begins breathing.
In an alternative aspect, the means for allowing air into the downstream region comprises a pressure-responsive valve at the downstream region. The pressure-responsive valve allows air into the downstream region when the pressure in the downstream region falls below a threshold level, usually in the range from xe2x88x923 cm H2O to xe2x88x9230 cm H2O. The pressure responsive valve is advantageous in allowing ventilation to be provided to the patient while still employing the diaphragm to enhance the extent and duration of negative intrathoracic pressure. Examples of pressure-responsive valves that may be used include, for example, a spring biased valve, an electromagnetically driven valve, or a valve constructed of any deflectable material that will deflect when the threshold pressure is exceeded. As one specific example, the valve may be constructed of a magnetically charged piece of material with a narrow tolerance that is attracted to a gate. This valve will open when the magnetically charged gate pressure is exceeded. In this way, when the negative intrathoracic pressure is exceeded, the valve will be pulled away from the gate to permit gases to flow to the lungs. Such a valve could also be used in place of the diaphragm valve discussed above.
In one option, a source of oxygen-enriched gas may be coupled to the pressure-responsive valve to supply an oxygen-enriched gas to the patient when the pressure responsive valve is opened. A regulator may be employed to regulate the pressure and/or flow rate of the gas. For example, the pressure may be regulated to be less than the actuating pressure of the valve so that the pressurized gas will not flow to the patient""s lungs until the valve is opened when the negative intrathoracic pressure is exceeded.
The system of the invention in another aspect is provided with an air exhaust opening in the housing at the upstream region for exhausting air from the housing. A valve is provided in the exhaust opening which inhibits air from flowing into the housing through the exhaust opening. In this manner, air exhausted from the patient is in turn exhausted from the housing through the exhaust opening. In a further aspect, means are provided for preventing air from exiting the housing through the exhaust opening during injection of air into the housing when ventilating the patient. Preferably air is injected into the housing from a respiratory device, such as a respiratory bag, a ventilator, or the like, or by mouth-to-mouth breathing through a port or a mouthpiece.
In still a further aspect of the invention, an endotracheal tube, a sealed facial mask, a laryngeal mask, or other airway tube, or the like is provided and is connected to the housing at the downstream region for attachment to the patient. The endotracheal tube or like device is for insertion into the patient""s airway and provides a convenient attachment for the valving system to the patient.
The invention further provides an exemplary device for increasing cardiopulmonary circulation that is induced by chest compression and decompression when performing cardiopulmonary resuscitation. The device comprises a facial mask and a housing that is operably attached to the mask. The housing includes a mouth piece and at least one inflow valve which prevents respiratory gases from entering the lungs until a threshold negative intrathoracic pressure level is exceeded at which time the inflow valve opens. The housing further includes an air chamber in communication with the mouth piece, and a valve member to force air from the air chamber and into the facial mask when air is supplied through the mouth piece. In this way, a rescuer may blow into the mouth piece to periodically ventilate the patient with air or oxygen-enriched gas stored in the chamber, rather than introducing respiratory gases from the rescuer""s lungs.
In a similar vein, the invention provides an exemplary method for increasing cardiopulmonary circulation that is induced by chest compression and decompression when performing cardiopulmonary resuscitation. According to the method, at least one inflow valve and an air chamber are interfaced to a patient""s airway. Chest compression and chest decompression is then performed, with the inflow valve preventing respiratory gases from entering the lungs during decompression until a threshold negative intrathoracic pressure is exceeded. Air is periodically transferred from the air chamber into the patient""s lungs so as to properly ventilate the patient with air. In one exemplary aspect, the air is transferred from the air chamber to the patient""s lungs by manually blowing into the chamber. In this way, the rescuer may blow into the chamber to transfer air to the patient""s lungs without introducing respiratory gases from the rescuer""s lungs.
In one embodiment, the invention provides a mechanism to vary the actuating pressure of the inflow valve. In this way, the rescuer is able to operate the mechanism to vary the impedance depending upon the condition of the patient. In some cases, the valve systems of the invention may include a pressure gauge to display the intrathoracic pressures. By having this information readily available, the rescuer has more information to assist in setting the desired actuating pressure of the inflow valve.
In one aspect, the varying mechanism is configured to vary the actuating pressure to a pressure within the range from about 0 cm H2O to about xe2x88x9230 cm H2O. In another aspect, the inflow valve comprises a shaft having a seal that is configured to block an opening in the housing, and a spring that biases the seal against the housing. With such a configuration, the mechanism may comprise a knob that is movable to vary the biasing force of the spring. For example, the knob may be rotatably coupled to the shaft so that the rescuer may simply turn the knob to vary the actuating pressure.
In another embodiment, the valve systems of the invention may be provided with a safety ventilation passage. If the valve system is inappropriately applied to a patient who is spontaneously breathing, the patient may breath through this passage while the valve system is coupled to the patient""s airway. A safety mechanism is used to maintain the safety ventilation passageway open to permit respiratory gases to freely flow to the patient""s lungs until actuated by a rescuer to close the safety ventilation passageway. With such an arrangement, the patient is able to freely breathe if they are capable of so doing. If the patient stops breathing on their own, the rescuer may set the valve system so that the ventilation passage is closed and the inflow valve provides the desired resistance during CPR. In this way, respiratory gases are permitted only once the cracking pressure of the threshold valve is exceeded, or when the patient is actively ventilated. As with other embodiments, the cracking pressure may be exceeded by decompressing the patient""s chest during CPR, by the patient""s own inhalation, or the like.
In one aspect, the safety ventilation passageway is provided through the inflow valve when the inflow valve is in an open position. With this configuration, the safety mechanism is configured to maintain the inflow valve in the open position until actuated by the rescuer to move the inflow valve to a closed position. A variety of ways may be used to actuate the safety mechanism. For example, the housing may include a ventilation port to permit respiratory gases to be injected into the housing, and the safety mechanism may comprise a sensor to sense when the rescuer injects respiratory gases into the housing. In one embodiment, a signal from the sensor is used by a control system to move the inflow valve from the open position to the closed position. As an example, the sensor may be movable upon injection of respiratory gases into the housing, and the control system may comprise a set of gears that are coupled to the sensor and a cam that is movable by the gears to close the inflow valve. Alternatively, the control system may comprise an electronic controller, a solenoid and a cam. This mechanism may be configured to take electrical signals from the sensor and to operate the solenoid to move the cam and thereby close the inflow valve. As another example, a flap may be moved upon injection of the gases. The flap may cause the movement of a variety of mechanical components that physically reset the inflow valve to the closed position.
A variety of sensors may be used to sense injection of the respiratory gases. For example, sensors that may be used include electronic switches that move in a gas stream, thermistors to sense temperature changes, CO2 detectors, materials that experience a change of resistance when flexed, mechanical flaps that move in a gas stream, and the like.
The invention also provides methods for increasing the blood pressure in a spontaneously breathing person. According to the method, a pressure responsive inflow valve is coupled to the person""s airway and the person inhales and exhales. During inhalation, the inflow valve prevents respiratory gases from entering the lungs until a negative intrathoracic pressure level in the range from about 0 cm H2O to xe2x88x9220 cm H2O is exceeded at which time the inflow valve opens. In this way, the inflow valve assists in increasing blood flow back to the right heart of the person and thereby enhances the person""s blood pressure. Such a process may be used to treat a variety of conditions where the person""s blood pressure is low. For example, such a procedure may be used where the person has low blood pressure due to blood loss, due to the administration of a drug, due to a high gravitational state, due to vasodepressor syncope, or the like.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.